One thing that changes all the time is the weather. And even the climate
(average of weather over a year)
changes over long periods of time. There have been times in the four
billion year history of the earth where nearly the whole earth was covered
with ice. There have also been very warm periods where there were tropical
plants and alligators at the south pole. Fortunately for humans, the
climate has been very stable over the past 10,000 years, since the end of the
last ice age. These years include the beginning of the agricultural
revolution and the birth of civilization.

Nearly all climate scientists agree that the main cause of this
warming is greenhouse gases, particularly carbon dioxide (CO2) released
from burning coal, oil, and natural gas. CO2 is called a greenhouse gas
because it's like the glass in a greenhouse that traps heat so plants
can grow even in cold weather. CO2 acts like a thin coating of glass
around the earth, keeping us from getting too cold. We're lucky to have
it, since it keeps earth from being too cold. But increasing the CO2
is like making the glass coating thicker and trapping more heat. CO2
has risen from 280 parts per million (ppm) in the atmosphere prior to
the industrial revolution starting around 1800, to 394 ppm as of 2012,
and is rising by about 2.3 ppm every year as we continue to burn
fossil fuels.

Gradually increasing CO2 is an example of quantitative change.
So far, the impacts of this CO2 have been manageable for most of us
earthlings, but the question is how long can this go on? An extreme
example of too much CO2 is the planet Venus, where the CO2 level is
hundreds of times higher than on earth and the average temperature is
around 457 degrees, hot enough to melt lead. (See:
Realclimate.org--Lessons from Venus)

If you sit in a car on a hot day in the sun with the windows rolled up,
you quickly come to a turning point
when you feel too hot. The normal solution to the problem is to roll the
windows down, or turn on the air conditioner. The question for earth
is, "When are we too hot?"

No one knows exactly when we will hit a turning point that will mark
a qualitative change for civilization, but the international scientific
consensus, ratified in Copenhagen, Denmark in December, 2009, is that
temperatures must not be allowed to rise more than 2 degrees Celsius
(about 3 1/2 degrees F) to "stave off the worst effects of climate change." (See:
press release from the UN Climate Change Conference in
Copenhagen).
These "worst effects" are truly horrible--droughts across much of the world,
floods, storms, heat waves, millions if not billions of deaths.
See www.350.org or www.climate progress.org to connect the dots for many of the
impacts of global warming around the world.

Similarly, no one knows exactly what level of CO2 in the atmosphere will
lead to this disastrous turning point. Leading U.S. climate scientist James
Hansen has estimated that 350 parts per million is an upper safe limit.
Some groups feel that 450 ppm would be acceptable as an upper limit, and some
people feel that a doubling of the pre-industrial level to 560 ppm would be OK.
However, most climate models indicate that even 450 ppm would likely exceed the
2 degrees Celsius temperature increase.

Even worse, if we don't stop the increase in CO2, earth itself could reach
some qualitative turning points. For example, as the earth heats up, the tundra
releases methane gas, an even stronger greenhouse gas than CO2. And this can become
a vicious spiral where more heat releases more methane gas, which then creates more
heat. This could cause the climate to spiral out of control, which happened at least
once in earth's history, 250 million years ago, although the exact cause is still under
debate. Apparently back then the earth became so hot and
miserable that 90% of all life forms died. It is very unlikely that humans could survive
such a devastating event if it were to happen again. See the book by
Michael J. Benton: "When Life Nearly Died, The Greatest Mass Extinction of all Time", for
more about this catastrophe.

Given that such horrific outcomes are a real possibility, we need to be taking every possible
precautionary step to reduce CO2 emissions.

We can't just roll the windows down on earth, but we can use alternatives to fossil fuels--wind,
solar, and hydroelectric power for clean, renewable energy. We can also use electricity to power our cars
(see my blog
Solar Power and Electric Cars) for more discussion of this.
We can build more energy efficient
buildings that consume less natural gas for heat, and we can do much more.
Altogether this is an enormous challenge, and it will take
all of humanity to work together to solve the problem. Maybe you will be the one to find a better battery, a
better solar panel, a way to produce fusion energy, a way to clean carbon dioxide and methane (another greenhouse
gas) out of the air, or other ways to address this problem!!

What we need is a turning point where masses of people recognize the problem and work to solve it.
We are already experiencing serious extreme weather events, and this is only going to get worse.
Unfortunately the major media are still controlled by people who support the oil companies' viewpoint
that global warming is not really a problem, and that the climate scientists are alarmists. When the
big corporations who control the media understand that their livelihood depends on stopping global warming,
I think we will see a dramatic turning point. All of us should work to educate people and build a mass
movement to support clean energy and clean transportation, and demand an end to the use of fossil fuels. Every
single voice adds up to a very loud shout--and that's when real change happens.